This invention relates to the field of document printing/copying. More particularly, it relates to improvements in apparatus for precisely positioning an electro-optical printhead or xe2x80x9coptical writer,xe2x80x9d e.g. a linear array of light-emitting diodes, relative to a reusable image-recording drum in a document printer/copier, that is, an electrophotographic printer and/or copier, so that a line of picture elements (pixels) can be imaged on the drum surface at a desired image location.
The above-referenced U.S. application Ser. No. 09/574,054 discloses an electrophotographic document printer/copier comprising apparatus for positioning a solid state optical writer, such as a linear array of selectively energizable light-emitting diodes, relative to the photoconductive surface of an image-recording drum. In the document printer disclosed, both the optical writer and photoconductive drum assembly share a pair of mechanical fiducials, in this case dowel pins, to locate these subsystems in the printer frame. The ultimate position of the optical writer is determined by the engagement between the respective outer surfaces of the two dowel pins and a pair of V-notched blocks carried by opposite ends of the writer frame. In this printer, tight tolerances must be adhered to in order to achieve sharp focus of the image pixels projected by the writer onto the photoconductive drum surface, as well as to assure that the projected line of pixels is not skewed with respect to a desired image line on the drum surface. Such high tolerances are especially necessary in the case the printer comprises one of a plurality of printer modules used in a multicolor printer to produce three or four color separation images that are sequentially transferred to a single receiver sheet in perfect registration with each other. In a multicolor printer, it will be appreciated that each of the optical writers of the different print is modules must be precisely located relative to the imaging drum to ultimately achieve the requisite registration of color images.
While the apparatus disclosed in the above-noted application is capable of meeting the optical focus requirements required for sharp imagery, it does not lend itself to skew adjustment. Owing to the engagement between the V-notched blocks of the optical writer frame and the outer, lateral surface of the dowel pins, any lateral movement of one end of the writer to correct for a skewed image line is prevented. Thus, only through the use of shims and the like inserted between a V-notched block of the writer and the dowel pin can skew adjustment be achieved. While this scheme may suffice for monochrome printers, a finer and continuous adjustment scheme is required to achieve sharp images in a multicolor printer.
In view of the foregoing discussion, an object of this invention is to provide improved skew adjustment apparatus for controlling the position of an image line on a recording element used in a printing apparatus of the type described.
The apparatus of the present invention is useful in an electrophotographic printer/copier of the type comprising: (a) a frame; (b) a drum assembly including a rotatably mounted drum having a photosensitive outer layer upon which a plurality of work stations operate to produce an image; (c) an optical writer for projecting a rectilinear line of image information onto the drum""s photoconductive surface as the drum rotates; and (d) a pair of mechanical fiducial mounteds on the frame, each fiducial being engaged by both the drum assembly and the optical writer to locate such subsystems on the frame. According to the invention, apparatus is provided for (a) pivotally mounting a first end of the optical writer on one of the mechanical fiducials for pivotal movement thereabout, (b) slidably mounting a second end of the optical writer for sliding movement atop the other mechanical fiducial, whereby the skew of an image line projected onto the drum surface by the optical writer is readily adjustable, and (c) selectively clamping the second end of the optical writer at a desired location on the second fiducial. Preferably, a micrometer-like mechanism is used to finely control the sliding movement of the second end of the writer atop the second fiducial.
As a result of the invention, the aforenoted disadvantages of using shims and the like to make skew adjustments in printers of the type described are avoided, and any skewing of the image line projected by the optical writer can be adjusted xe2x80x9con the flyxe2x80x9d while the printer is in operation.
The invention and its technical advantageous effects will be better appreciated from the ensuing detailed description of a preferred embodiment, reference being made to the accompanying drawings in which like reference characters denote like or functionally similar parts.